


An Antidote to Uncommon Poisons

by masterofesoterica



Category: Harry Potter - J. K. Rowling, Sherlock (TV)
Genre: Alternate Universe - Canon Divergence, Alternate Universe - Fantasy, Bullying, Crossover, F/M, Gen, Magic, Oral Sex, Romance
Language: English
Status: Completed
Published: 2014-08-07
Updated: 2014-08-19
Packaged: 2018-02-12 04:59:29
Rating: Mature
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 2
Words: 4,731
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/2096637
Author URL: https://archiveofourown.org/users/masterofesoterica/pseuds/masterofesoterica
Summary: <blockquote class="userstuff">
              <p>Molly Hooper may hold the answer to Mycroft's questions following Sherlock's demise.</p><p>Featuring: bonding over Toby the cat.</p>
            </blockquote>





	1. Chapter 1

**Author's Note:**

> I never meant to write Molly/Mycroft but their cuteness grabbed me and wouldn't let go until this was written.

_Eliminate all other factors, and the one which remains must be the truth._ Or the key to truth, in this particular instance. But this particular remaining factor, rather vexingly, was human, and therefore not always accountable to the truth.

Mycroft tapped his wand against the blank stretch of parchment, and a spiral of ink unfurled itself into neat lines of text. Before him lay the dossier of one Molly Hooper. In the vast net of arithmancy and runes that Mycroft always held in his head, she was the lone cluster of symbols and equations related to his brother’s case that he had not already examined and rejected.

The dossier contained information of Molly Hooper’s magical signature throughout the years. Up until age seventeen was easy of course; under his supervision the Trace had been significantly modified not only to trace all magic performed by underage magic users, but to detect suspicious or otherwise alarming tendencies in particular children too. Her file revealed no striking peculiarities—nothing at all to suggest that she had been anything but a perfectly adequate and average witch. Once a witch or wizard came of age, it was rather more difficult to track them. Sometimes, Mycroft truly envied muggle governments with their eyes and ears in every nook and cranny, in every street and parlour, in every ingenious machine.

Magic was altogether more volatile. It resisted containment; its nature was a slippery one. A piece of magic did not just stay still; it pervaded its surroundings in certain patterns and forms. Magic denatured its core until all that remained were afterimages of the magic itself with no sign of the caster. Except that that was not entirely true. Mycroft had, from infancy, recorded these afterimages in his mind—modelling them with a complicated series of knitted equations, overlaying them so that the source underneath began to emerge. And so he knew of every piece of magic in Britain, and quite a few abroad, and made himself indispensible to the world at large, though few knew it.

And yet, here it was. An absolute void where there should have been _something_. A rend in the fabric. Ever since Sherlock. This Molly Hooper was completely unremarkable, and yet, somehow she was connected.

Mycroft retreated to his considerable mind palace and brought to hand what he knew of her. He remembered her from his time at Hogwarts, although only briefly. He had been a seventh year prefect when she’d arrived, small and plain and rather unremarkable. He made a habit of always sitting near the head of the Ravenclaw table at the Sorting Feast, to better gauge the new students. Girlish muggle clothes beneath her new robes, but clearly some familiarity with magic—a half-blood then. Observing her timid nods as the other first years chattered in the line, he pegged her as a Hufflepuff, or perhaps Ravenclaw—she seemed as though she had some brains beneath all her nervous tics. When she was sorted into Gryffindor, he’d been surprised—she was the only one of the firsties he’d misjudged.

Perhaps he hadn’t been observant enough, he surmised. He’d been focussing most of his attention on his brother, standing there with a little furrow in his brow.

Mycroft had been reminded of his own Sorting too: he hadn’t been nervous, and he’d left nothing up to chance—not as Sherlock was doing. Well, Mycroft had always been the smart one in the family.

The Sorting Hat had made its decision within a second of touching Mycroft’s head, but he’d made it shut up before it could proclaim its judgement to the entire school. He was in it for the long game, and couldn’t have some stupid slip of cloth mess it all up. However venerated it was, it was only haberdashery.

“I’m not going there,” he had told the hat firmly, “whatever you’ve got to say, save it.”

The Hat laughed, if it could laugh. “It is where you belong. You could do very well there you know, very well indeed. Your housemates could be your family.”

“I won’t threaten you; you’re a hat. But I have heard about you. I’ve chosen, see, and you’re not going to get in my way.”

“Very well. If that’s the case, then it’d better be—Ravenclaw!”

Mycroft had slid off the stool and made his way unhurriedly to his table, greeting his fellow students with a rather triumphant smile.

 

\---

 

Molly Hooper had not attempted to hide herself. She was quite simply there, for anyone to seek out, in the laboratory behind Bartholomew’s Apothecary in which she worked. The laboratory did not even have doors—a distinct safety hazard, Mycroft noted, given the volatile materials in there which would have a rather destructive effect if they were to come into contact with any of the pre-bottled potions resting in the shop. But that was none of his concern.

Presently, he was concerned with the tangle of equations that was this woman of flesh and blood.

He had already notified her by owl of his planned presence, and saw it fit to dispense with formalities. She was not brewing, merely preparing ingredients. A shining brass cauldron stood empty in one corner of the workbench.

“Miss Hooper, if I may ask you some questions?”

“You’re the one who owled. Oh, who are you? I mean, I think I remember you. From Hogwarts—or, no, maybe that wasn’t you,” she halted the steady movements she had been making with the mortar and pestle, and looked up at him with slightly squinted eyes. He would’ve found it comical.

“You are not mistaken,” he said curtly, “Mycroft Holmes, Under-Secretary to the Departmental Head of International Magical Cooperation.” (That was what it said on his cards and office paper and letterheads, at any rate. But usually, his name was all anyone needed to see.) He did not proffer his hand.

“I see.”

“If I may ask you a few questions?” he said again.

“Oh yes, of course.” She fidgeted nervously, pulling at the hem of her jumper.

“Have you any knowledge of the last moments of the fugitive Sherlock Holmes?”

“It—it happened just outside, in broad day light. I saw only what other passers-by or—or shopkeepers saw. I was in this lab. Then I rushed out when people began to scream for help.”

“And beyond that? I understand you assisted the healers in the immediate aftermath? And you had no further contact with the bodies?”

“No, no. Definitely not.”

“He used to frequent this apothecary, did he not?”

“Yes. Um. That is, he was a customer here. Before his—uh—before the events…that happened,” she was not telling the entire truth, it was plain to see, and her attempt at nonchalance was feeble.

Mycroft decided that this mode of inquiry was not conducive to eliciting answers. He switched his tone. “So, Miss Hooper, or Healer Hooper, is it not? I understand that you are also engaged at St. Mungo’s on a casual basis.”

“Er—yes, only when there’s been a suspect death, usually by poison—I’m good with the more lethal poisons.” She hastily backtracked, “I mean, I can identify their effects. But I prefer it here in my lab though, when there’s only the mice or Derek to talk to. Oh, Derek’s—”

She trailed off into a nervous giggle and pointed at the life-sized simulacrum of a body that rested on a long bench in the far corner of the lab.

“I don’t like to use the mice—for the poisons, the painful ones—Derek’s much better. His vital organs just light up like Christmas when the potions are just right. It’s quite brilliant, Derek shows pain and decay and death.” She stopped as though she’d just realised what she’d been saying, “Oh no, but just research—oh—I shouldn’t have said all that—I don’t sell them. The poisons, not Derek. You won’t…”

“Rest assured, Healer Hooper, it is not my department.” Mycroft felt no need to further threaten the girl with Ministry sanctions; she had fidgeted rather tellingly when he’d asked her about her job at St Mungo’s slicing up cadavers. And the simulacrum was certainly a piece of spellwork to be admired. He certainly had enough data to be getting on with. Then, quite suddenly, and unbidden, another memory came to him.

“You have always been rather concerned with the welfare of—defenceless—creatures, as I recall.”

She must have recalled it then too, for she looked at him with a startled expression. A nervous giggle bubbled up her throat, but her mouth curled in a rather more sincere manner.

Sometimes after the Christmas holidays in her first year, the Potions Mistress had decided to introduce her first year class to the practices of a potioneer. She believed strongly in the proprieties and traditions of magic. And so it happened that on that particular day, Molly was required to feed distinctly off-colour Swelling Solution to a tabby kitten that had been supplied to her by the professor, since she did not have her own familiar. Molly hated cats: their squashed little faces and their sharp little teeth. She was scared of them—ever since she had been scratched by her squib neighbour’s vicious Burmese some years ago. She still bore the scars from that encounter on her forearms, long curving silver lines.

Molly could not do it. Her Swelling Solution was subpar, she knew that. She had added too much daisy root and too little beetle eye and her shredded liquorice root had been far too coarse. She could not do it. Her hand shook terribly as her professor stood over her, glaring down at her with cold hard eyes, disparaging her silently for her weakness.

It was the practice of any trained potioneer to test their work on animal familiars. What had she to balk at? Potions was Molly’s favourite subject, though not her best one. She hoped to brew potions for a living; she hated to disappoint her professor. There were eyes on her now. She heard several Slytherin boys muttering. Molly felt smaller than ever—small and stupid and anything but brave.

She could not do it: she could not pick up the kitten, nor could she feed it her inadequate potion. Molly stood there, paralysed, for what seemed like hours with all the eyes in the class trained upon her. She was only saved by the bell ringing the end of class. The Potions Mistress picked up the kitten by the scruff of its neck, vanished the contents of her cauldron, scrawled a ‘D’ in her grade-book beside Molly’s name, and shook her head at Molly. Some of her fellow Gryffindors gave her pitying looks as they preceded her out the door.

That evening, two Gryffindor boys—one older boy and one first year—and a girl accosted her in the common room.

“We need to talk,” the first year boy said, with a glint in his eye, “come with us.”

This was all very strange; Molly didn’t usually speak to anyone much in her house. They were all too loud to notice her. She preferred to study with a group of Ravenclaws and Hufflepuffs and Slytherins in the library. Only Meena of the girls in her dorm had paid her any attention. These housemates could not mean her harm, she supposed. Molly gathered her books and her wand, and followed them out the Fat Lady’s portrait down to an unlocked classroom in the dungeons. Immediately, she knew what they meant to do.

“You made an absolute mockery of us in Potions today, little Molly Hooper.”

“Little Molly mouse, scared of a little kitten—you’re not fit to be in Gryffindor!”

“Merlin, you’re pathetic!”

There was a purr; the girl strode to a box in the corner of classroom and pulled out the kitten that had been the source of her humiliation and shame earlier that day.

“Take it!” the elder boy ordered, drawing his wand and pointing it at her chest. Surely he didn’t know any spells that could cause her too much harm. But then, he was a fifth year.

She turned to the squirming mass in the other first year girl’s arms, and tried hard not to wretch. It was only a cat, and a larger version of it was on their house crest after all. Molly held out her arms; the ball of fur was deposited into her hands. She couldn’t stop herself from flinching. But the kitten was still and did not make a sound. She could feel its ribs, the soft flesh and the pinkish pads of its paws. It was not so bad. It looked up at her with strange pale yellow-silver eyes, and felt some of her nervousness disappear.

“Now feed it this.” The fifth year held up a phial of unlabelled potion. “You want to be a _real_ witch, don’t you?”

“No, I can’t,” she said, “I don’t know what it is! What if…”

“Scared, are you?” said the girl. “Oh, poor mousey half-muggle Molly—so where’s the house for little mice like you?”

“I can’t…I won’t,” she was crying now, fat silent tears coursing down her cheeks and dripping down her collar.

“Do it,” the younger boy said with a sneer, holding his want to the side of Molly’s neck, and pressing the uncorked glass phial into her hand.

Molly stares into those round pale eyes and felt bile rise up in her throat. “I’m sorry…I’m sorry…” she sobbed, holding the kitten close to her chest, and no longer afraid of its claws or teeth.

The girl forced the jaws of the kitten open and stared at Molly expectantly. Molly’s hand shook as he lifted the phial up, the potion sloshed out of the phial and slid down the throat of the creature. With a gasp, she threw the potion away from her. A thick cloying wave of guilt was suffocating her.

“Good,” said the boy, retracting his wand and following the others out the door.

Molly was crying harder than ever; she sank to the floor, clutching the tabby to her. The poor kitten let out a scream of anguish—its body began to writhe and shudder in her arms, its limbs bulging and twisting and contorting. No-one deserved to die in such agony, she thought, and no-one deserved to die without a name.

“Toby, shh,” she whispered, pressing her nose to his side, and stroking his ears, “it’ll be okay, Toby.”

And that was how Mycroft had found her, sprawled on the stone floor, cradling a misshapen mass—her face red and swollen, tears and snot everywhere. Mycroft had been disgusted to see how an eleven-year-old girl could look like such a bloody infant. He’d never seen anything so pathetic.

He’d crouched down in front of the crying girl and pressed a clean handkerchief into her hand. Then he’d taken the cat and placed it on one of the benches, running a series of diagnostic spells over the contorted body.

“Will Toby be okay?” she had asked between hiccups, the square of white linen pressed to her face.

“Toby?” he had muttered incredulously.

And then of course the whole sorry tale had spilled out while he identified the potion fed to “Toby”, and neutralised its effects with a spell, vanished it from the feline’s system, and reset the deformed bones. He began to intone the spells aloud when he noticed how closely she was watching him, and performed his wand movements with exaggerated care. He had been flattered at her attention, and there had been a part of him that did not relish lingering in shadows. Eventually, the kitten had been restored to his former state of health—though a few healing spells had to be performed several times over. Mycroft cast a final sleeping charm over the tabby cat and he’d stood back, pleased.

“Oh thank you—er—”

“There’s no need. I’m a prefect and it is my duty—”

But she had already thrown her arms around his middle with undisguised delight. He stood, frozen and awkward for a few seconds before extricating himself from her grasp.

“I’m sorry, I’ve ruined your handkerchief—oh, thank you for helping Toby—I…” She beamed so brightly up at him that he had had to turn away.

“Quite all right. Now, it’s past curfew and you should be getting back to Gryffindor Tower.”

Molly had scooped up the slumbering Toby in her arms and trailed Mycroft all the way back to the Fat Lady’s portrait, and thanked him again.

They had not traded another word again in his time at Hogwarts. And if those three Gryffindor students avoided Molly from that day on and looked at her new familiar with something akin to fear, then how was Mycroft to know anything about _that_.

Mycroft was not surprised that this particular memory had been assigned to the deepest bowels of his mind palace. It irritated him that it had surfaced so uncontrolled to the foremost of his mind. Discipline, he reminded himself. He was ice: hard and crystalline; there were no fractures in his mind, no spot of cloudy imperfection, and no sign of anything more beneath the transparent surface.

Molly Hooper, without ever having said as much, had given Mycroft the last pieces of the puzzle. Already, he was re-knitting the net, fastening together the frayed edges of the rend, unravelling the pool of threads that was Molly Hooper, pulling her towards the empty centre, pulling Sherlock’s equations with her.

“Thank you, Healer Hooper, you have been most helpful. My most sincere regards.” He inclined his head, not so much that it could have been a bow. “I am certain we shall meet again.”

Molly stilled for a moment, considering the faint promise in his tone. Then she smiled, her brown eyes crinkling, and picked up her pestle once more.


	2. Chapter 2

**Summary for the Chapter:**

> Mycroft comes to Molly seeking absolution.

They did indeed see one another again. Many times.

Mycroft turned up one day to look at a middle aged old man who had seemingly overdosed on a medicinal poison and ended up on her bench, and declared it murder. One body became multiple bodies—all of them mysteriously linked to Sherlock, of course. Soon these visits became long, meaning-filled silences over tea and biscuits, where she stared at him over the rim of her teacup but always felt a little out of her depth, first in the St Mungo’s canteen, and then at various out of the way tea shops. These teas soon became dinners, and it was all very well done, very deftly done indeed, because soon enough indeed, one night after dinner, she was inviting him into the little flat she kept in muggle London, and he was fucking her on her mother’s scratchy, corduroy sofa.

Molly had no doubt that every last detail of her seduction (for it was clear that’s what it had been) had been scrupulously planned—and she wondered, dully, if she had surprised him at any point. She didn’t mind if she didn’t. It felt good to let go, to let Mycroft pull her into some distant corner of his orbit, to let him guide her. Soon, they had fallen into a mutually pleasurable pattern. Mycroft was as meticulous in sex as any other part of his meticulously organised life, and viewed any unsatisfied desires, spoken or unspoken, in his partners as a personal failure, almost an affront. Their relationship was uncomplicated, and Molly, who had often been disgusted by her own weakness, her incapability of compartmentalising her emotions, prided herself in the divorce she maintained between her life—and Mycroft. She dated Tom and did not feel guilty. She chatted about Tom’s rather endearing lovemaking with Meena and Caroline and did _not_ feel guilty.

\---

It was a Sunday, Molly had showered and dressed in her most comfortable pyjamas, prepared to spend a day curled up on the couch with a potions journal and the television—and in the afternoon, she would perhaps try her hand at a new recipe for scones that she had borrowed from Caroline. Just as she sat down at her kitchen table with a bowl of muesli and the Daily Prophet, there came a familiar rapping at the door.

Mycroft never came here without sending word before. But it was undeniably him; she could hear the wet tap of his umbrella. Her wards were thrumming with recognition of his magic. Again he knocked, firm but insistent. Throwing on a warm dressing gown over her flannel pyjamas, she shuffled to the door. Her hair must have been a mess, curling in damp tendrils around her face, but it didn’t matter—he must have had some rather drastic reason to visit her here at this hour, so out of keeping with his normal manner.

“Mycroft, what—what are you doing here?”

He didn’t reply, but brushed past her, striding into her kitchen and pulling out her bottle of firewhiskey from its hiding place behind her medicinal potions. Obligingly, she followed him, and produced two glass tumblers. Still, he avoided her gaze as he poured the amber liquid.

“A little early for a drink isn’t it? I’m only just having breakfast,” she said, gesturing to the bowl of muesli that she had been eating. His silence irritated her and crawled beneath her skin like some deformed parasite, gnawing at her flesh; it felt like the silence before an inevitably terminal diagnosis. She wondered if it had anything to do with Sherlock. Of course, logically, for all intents and purposes, Sherlock should’ve been fine. He had John to protect him, and Lestrade, and the whole wizarding public who’d seemed to have forgotten all about the unfortunate accusations and Moriarty. But still she worried. Her worry for him was a habit—an addiction—ever-present, lurking beneath a thin veneer of rationality, and always ready to prey upon her weakness.

“Please,” she said, her voice catching, “please, just tell me—”

Mycroft looked at her then, with something undeniably tender, and yet fragile and uncertain, struggling to pierce his icy exterior. She was frightened by the unfamiliarity of this situation. She was accustomed to the Mycroft who was cold, whose eyes were dark with lust for her, but whose lips were ever compressed into a thin line. She knew that Mycroft whose face held back the vast reservoir of his emotions like a dam. That Mycroft had comforted her with his coldness, with his disregard for her. She hadn’t counted—she hadn’t minded.

But here the same man stood, his lips trembling, his grey eyes glazed, his forgotten glass set down untasted on the bench. She did not know this stranger. He kissed her, a gentle pressure of the lips that was at once chaste and electric. Molly felt her knees give. He had never tasted like that before—like earl grey and lemon and something infinitesimally bitter. She fell back with a little gasp into the hard edge of her kitchen bench, threading her hands around his neck and pulling him closer, the pain at her back steady and pleasant. His mouth was on hers again, suddenly almost punishing in his forcefulness. The other Mycroft had always kissed her with a sort of efficiency, as though she had been a complicated lock to be unpicked. Now, he was pulling her apart altogether.

His neck was so very delicate under her hands. She memorised the slopes of his cheek and jaw, the soft stubble that she’d never before felt against his cheek (and that was only the last in a long line of surprising things). She could feel the protrusion of each segment of bone beneath slightly freckled skin, and the downy hair that curled at the nape of his neck. By now, had she the desire to do so, she could have killed him many times over. Instead, tugging at the front of his coat, Molly drew them both towards her bedroom. Even the wool of his coat felt different. It smelt damp from the rain. Mycroft’s clothes did not ever fall prey to things as plebeian as the weather: they always fit smoothly against his skin, thickly woven with as many spells as threads.

“What’s wrong,” she murmured again, as his lips moved to her neck and down to her collar, “why don’t you tell me.”

“I need you,” he said at last, his voice a guttural rasp.

He was unbuttoning the front of her flannel pyjama top; it occurred to her to be embarrassed a little, at the childish pattern of owls and moons that decorated her outfit, but she was far too distracted by what Mycroft was doing with his tongue. And he was still fully dressed, which hardly seemed fair. Molly put her worry to one side, and gave herself to feeling—to sensation.

Pulling his head back by his hair, a little roughly, she pressed her hand hard against his mouth and smiled a little, her white teeth gleaming. She was determined to see him, to strip him bare; and he would let her.

“Let me _see_ ,” she murmured into the leaden air between them. And she pulled the heavy woollen coat from his angular shoulders, and smoothed her hands over the lapels of his suit. It was rumpled. He watched her carefully in her ministrations, still with that unfamiliar almost-pain in his eyes. She removed each article of his clothing with a delicate grace and focus; it was as though she were back in her lab, peeling open the cavity of some cadaver’s chest, seeking for the heart, the gall, the bile underneath. He was so white, his skin translucent in places and the purple-blue veins like an incoherent map underneath. Her fingers lingered on the panes of his chest, his stomach, the curve of his flanks, where he was quivering. Was this vulnerability, she wondered, was this his obeisance, his capitulation—.

“Please.” He sounded strangled, ineffably weary.

She took his head in her hands, the short, auburn locks damp with sweat, pressed his face between her thighs. She was already wet. He kissed her, touched her with his tongue and fingers, unwound her one thread at a time. And she tasted sweet. Sweeter than he could have imagined; he felt as though he was sinking beneath the knife-edge of her sweetness. It was cutting some strange darkness from his flesh—a shade that he did not even know was there. The heat of her was white-hot against his lips.

She was perched at the edge of her bed, her hands twisted in her sheets, and she was keening with a voice that was almost inhuman. He felt each pulse of her racing heart, the blood that felt roiling and molten beneath her skin.

He pulled back; she felt the lack of him like something freezing and sharp. Her keening became mews of _want_. But then he was moving over her, and she was reaching between them, guiding his cock inside her until he’s buried up to the hilt. They moved slowly. She rocked him, cradling him with her arms and legs, his lips pressed to the sensitive spot behind her ear as they moved together. Molly felt the tight pool of heat within her build and swell, and soon it was crashing over her, and his mouth against her own tasted like her and she was licking the taste of her own cunt from his lips. A few seconds later, he too was coming, and his fingers were dug deep into the flesh of her back and there were red crescents there, and blood beneath his nails.

“I’m sorry,” he was saying, but she could barely make out the words beneath his laboured breaths, and beneath her own dawning bewilderment.

“Sorry,” she repeated faintly. She turned to face him, though not quite looking into his eyes. “What are you sorry for, Mycroft?”

“I—I’m—”

She has never heard him hesitate like this before, but he had been nothing if not surprising. The noonday sun slipped through the shutters and picked out the red-gold in Mycroft’s hair, and threw vertical shadows across his worn face.

“I forgive you,” she said simply. Molly stared into the pale irises of his eyes and reached out to touch the tops of his eyelids with her fingertips. “Whatever it is, I forgive you. Now—sleep.”

And he did.

**Notes for the Chapter:**

> I haven't seen BBC Sherlock for a while, unbeta'd, and I also haven't really written sex before. Apologies for any errors.


End file.
